Magnetic core



Oct. 26, 1965 D. c. GRAHAM 3,214,718

MAGNETIC CORE Filed Deo. 4, 1962 2 Sheets-Sheet 2 Jy M@ 742,@-

Oct. 26, 1965 D. c. GRAHAM 3,214,718

MAGNETI C CORE Filed Deo. 4. 1962 2 sheets-sheet 1 United States Patent O 3,214,718 MAGNETIC CGRE Donald C. Graham, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Filed Dec. 4, 1962, Ser. No. 242,143 4 Claims. (Cl. 336-217) This invention relates to magnetic cores and more particularly to improvements in laminated flat stacked three-legged magnetic cores for core type, as distinguished from shell type, stationary three-phase alternating current electrical induction apparatus.

Such c-ores are characterized by two alternated or interleaved sets lof layers which may respectively be referred to for convenience as a set of odd numbered layers and a set of even numbered layers although it makes no diiference which set is which.

Each layer is generally made up of the same number of identical sheets of laminations. The reason for using more than one sheet per layer is that it reduces the amount of labor involved in laying up or stacking the core. Each sheet of laminations generally has seven separate pieces of magnetic material, there being three parallel coplanar equally spaced leg pieces and four yoke pieces extending perpendicular to the leg pieces and joining the corresponding ends of adjacent pairs thereof. As a consequence of this construction each sheet also has eight butt joints between adjoining ends of leg and yoke pieces, the two joints at each end of the center leg being referred to collectively as a T-joint and the other four joints being called corner joints.

In order to reduce the magnetic reluctance of such a core the corresponding joints in adjacent layers are staggered or offset from each other in the direction of magnetic flux therethrough so as to produce an area of overlap. Because the magnetic pieces making up each sheet are generally made of highly grain oriented cold rolled silicon alloy steel cut to length from a rolled or coiled strip of such material they have a most favorable magnetic direction corresponding to their lengthwise dimension which is also the normal direction of magnetic liux therethrough. This staggering or offsetting of the joints can be accomplished by making the sheets of the layers of one set the same as the sheets of the layers of the other set and reversing the sheets or layers of one set relative to the other set such as by 180 degree-rotation on the longitudinal center line of the center leg.

In order to minimize deviation of the direction of flux in the pieces from their most favorable magnetic direction when iiux goes around a corner, the joints are usually so-called mitre joints. There has always been a problem with T joints because magnetic flux not only enters and leaves the vertical leg of the T in both directions in going from and to both outer legs, but it also goes directly through the horizontal top arm of the T in going between the outer legs. In other words, while the mitre joint is admirably suited to the corner joints, it is not as well suited to the T joints.

Another problem with such cores is that of waste of material in cutting the parts particularly at the T joints. This problem of scrap is accentuated by the realtively high price or cost of the material.

A further problem with such cores is the substantial number of different parts which are required.

. An object of the invention is to provide a new and improved magnetic core.

, Another object of the invention is to reduce the number of parts needed to make three-legged dat stacked cores of grain oriented magnetic strip material.

A further object of the invention is to minimize the waste or scrap produced in cutting parts of magnetic 3 ,Z 14,7 18 Patented Oct. 26, 1 965 lCC strip material for a three phase three-legged core while still retaining a high degree of mitering of the joints.

An additional object of the invention is to provide a novel core of the above-described kind having the same seven parts in each sheet of each layer.

A still further object of the invention is to provide a novel core of the type described above wherein seven separate pieces in each sheet of each layer are formed in an equal or lesser number of different geometric patterns, and the same patterns appear in each sheet of each layer.

In carrying out my invention in one preferred ernbodiment, I build up a laminated three-legged core out of seven separate lamination pieces in each sheet of laminations, the seven pieces having several different shapes or patterns and the same patterns being used in the sheets of adjacent layers but in reverse positions with respect to a predetermined core axis. The sheets of both layers are all edgewise coincident, i.e., fully congruent. The pattern of the center Ileg of each sheet is generally a parallelogram so that T-joints at opposite ends of the center leg are made up of one mitre and one square joint with the two yoke pieces adjacent each end of the center leg. Reversal of the center leg pat-tern in adjacent layers alternates the direction of its mitre cuts and this produces joint overlap by transposition of such mitre cuts. The outside leg pieces are mitred at both ends to form offset mitred joints at all outside corners of the core, the offsets being in such directions that reversal of these patterns and the adjacent yoke patterns in alternate layers produces offset overlap at all corner joints. The lamination patterns are so shaped that a full set of pieces for a single layer may be cut with no waste from a continuous strip of magnetizable material.

It is a feature of my improved core that six of the eight core joints in each sheet are mitre cut, so that the core may be referred to as a three-quarter mitre core. I-t is another feature that while both T-joints in each Vsheet are asymmetrical, they are so oriented that each sheet is symmetrical relative to the T-joints considered together.

The invention will be better understood from the following description taken in connection with the accompanying drawings and its scope will be pointed out in the appended claims.

In the drawings,

FIG. 1 is a perspective view of an embodiment of the invention,

FIG. 2 is a sheet of one of the alternate layers to that illustrated by the top sheet in FIG. l, while FIGS. 3 and 4 are illustrations, corresponding respectively to FIGS. 1 and 2, of another embodiment of the invention.

Thus if FIG. 2 or FIG. 4 is considered as having been removed from the front or top of FIG. 1 or FIG. 3 respectively, it can be considered a sheet of an odd numbered layer, whereas if it is considered to have been taken from the bottom `or back of FIG. 1 or FIG. 3 it can be considered as a sheet of an even numbered layer.

Referring now to the drawing and particularly to FIG- URES l and 2, I have shown a laminated magnetic core formed of two differently constructed layers L1 and L2 each composed of a plurality of identical sheets of grain-oriented magnetizable material. Each sheet is formed of seven laminat-ion pieces with the pieces difrerently arranged in the sheets of adjacent layers. The exposed sheet S1 of FIG. 1 shows 4the sheet construction of layer L1, and the sheet S2 of FIG. 2 shows the sheet construction of layer L2.

As shown in FIG. l, it is preferred to lay up or stack the core with four sheets per layer, but this is not an essential feature of the invention. The sheets shown in detail in FIGS. 1 and 2 are formed of the same set of patterns bu-t the pieces are alternately reversed about the longitudinal center line of an identical center leg part L. These sheets have seven different lamination pieces per sheet and each piece is of a different pattern, the same sevenpa-tterns being used in each sheet. Thus, in addition to the center leg piece L, there is an outer leg piece A, an outer leg piece X, a yoke piece B joining adjacent ends of leg pieces A and L, a diagonally opposite yoke piece Y joining adjacent ends of legs L and X, a yoke piece C joining the opposite ends of leg pieces A and L, and a yoke piece Z joining the opposite ends of leg pieces L and X.

The piece L is generally in the shape of a parallelogram with its ends at forty-five degrees to its sides except that the two corners on one side are respectively notched at 1 and squared at 2. The piece A isl generally in the shape of an isosceles trapezoid except that the corners on the long side are squared as indicated at 3, the square corners having the same dimension as the square corner 2 of piece L. The piece X is also generally isosceles trapezoidal in shape except that the corners at the ends of its short side are notched as indicated at 4, the depth or configurations of the notches 4 being the same as the notch 1 and also being of the same depth or transverse dimension as the squared corners 2 and 3. The piece B has a geometrical shape similar to the piece X but of different length. The piece Y has a geometrical shape similar to the piece A but of different length. The piece C has a squared end and a fort-five degree mitre end, the latter being provided with a notched corner 5 adjacent the short side thereof. The piece Z has a square end and a forty-five degree mitre and with a square corner 6 adjacent the long side thereof. Thus at FIGURE 1 While several of the separate pieces in each layer have similar geometric shapes, the seven separate pieces are in seven different patterns.

As a consequence of this construction, the mitre corner joints are all offset from a corner diagonal of the core running from the inner corner to the outer corner of the core and because of the reversal of parts in adjacent layers these joints are offset from each other in adjacent layers. Thus in FIG. l the upper corner mitre joints are shown offset in a counterclockwise direction from their respective corner core diagonals, while the lower corner mitre joints are offset in a clockwise direction from their corner core diagonals, whereas in FIG. 2, due to the reversal of the layers, the upper mitre joints are displaced clockwise and the lower mitre joints are displaced counterclockwise from their respective corner core diagonals. It will also be seen that the individual joints making up the adjacent T joints in superposed layers are also offset from each other. Also, in each sheet or layer the mitre joint of each T joint is on opposite sides of the center leg L, and the same is true for the squared butt joints of the two T joints.

Referring now to FIGS. 3 and 4 these are views, corresponding respectively to FIGS. 1 and 2, of a modification of the invention in which the number of different piece shapes, or patterns, has been reduced to six by using one of the patterns twice in each sheet. Piece L', the center leg of all sheets is of the same general configuration as part L of FIGS. 1 and 2 except that its ends are straight line 45 degree beveled instead of broken line beveled as indicated by the phantom lines representing the configuration of piece L. In other words, piece L is a pure parallelogram. The pattern of piece A'X is duplicated in each sheet of each layer and comprises the outer legs. While generally in the shape of an isosceles trapezoid like pieces A and X of FIGS. l and 2, it differs therefrom in that it has a single squared corner 3 on one end of the long side and a single notched corner 4 at the offset end of the short side. Thus piece AX is not symmetrical inthe sense that pieces A and X of FIGS. l and 2 are symmetrical. The third piece B is generally similar to piece B of FIGS. l and 2 except that its inner end adjacent the center leg is straight line beveled cut so as to match the corresponding beveled end of the leg L'. The fourth piece Y bears the same relation as piece Y to FIGS. 1 and 2 that piece B bears to piece B, i.e. its inner end is straight line beveled so as to match or make a 45 degree mitre joint with the adjacent end of the leg piece L. The fifth and sixth pieces C and Z have the same shapes or patterns, respectively, as the similarly lettered parts in FIGS. 1 and 2.

While FIG. 1 is structurally the same as FIG. 2, and FIG. 3 is the same structurally as FIG. 4, the orientation of FIG. 1 relative to FIG. 2 is different from the orientation of FIG. 3 relative to FIG. 4. As previously mentioned, the sheets represented by FIGS. 1 and 2 are reversed or rotated a half turn about the longitudinal center line of the center leg piece L or right to left as viewed in the drawings in order to obtain the desired offset or overlap of the transposed butt joints of different layers. This is a consequence of the use of different outer leg pieces in each sheet. However, the layers represented by FIGS. 3 and 4 are reversed or located a half turn about an axis through the center points of the three legs, or from top to bottom as viewed in the drawings in order to get the desired offset or overlap of the butt joints. This is a consequence of the duplicate use of the same unsymmetrical outer leg patterns in each sheet.

As the mitre joints of successive or adjacent layers in the T joints are not parallel, as they are at the corners, but actually intersect at right angles to each other, nothing is gained in the T joints by having offset or broken line mitre joints in the T joints, as in FIGS. 1 and 2, over having simple straight or unbroken line mitre joints as in FIGS. 3 and 4. Thus the T joints of FIGS. 1 and 2 can be made like the T joints of FIGS. 3 and 4 by cutting the pieces forming them along the phantom lines shown in FIGS. 1 and 2 instead of along the solid lines. Likewise if desired, the T joints of FIGS. 3 and 4 can be made like the T joints of FIGS. l and 2 by cutting the parts joining them along the phantom lines rather than along the solid lines. This does have an advantage in that the differences between pieces B and Y' disappear and they would become a duplicated piece BY which would be an asymmetrical isosceles trapezoid of the same shape but different length than the piece A'X.

The cores shown in FIGS. 1 and 3, of course, have rectangular cross section legs so that they are most suitable for linking electrical coils or windings having rectangular cross section windows. However, it will be obvious to those skilled in the art that cores of the same configuration as FIGS. 1 and 3, by using progressively different Width pieces, may be superposed on each other as is well known practice in making so-called cruciform cores which would then provide leg cross sections providing a better space factor in electrical coils or windings having windows of circular cross section.

The material of which the core parts and pieces are made may either be singly oriented (cube-on-edge crystal texture) or doubly oriented (cube-on-face crystal texture). In either case there is a most favorable magnetic direction corresponding to the lengthwise dimension of the parts or pieces and to the normal direction of fiux therein. However, in the case of doubly oriented material there is another almost as favorable magnetic direction perpendicular to the first one but parallel to the plane of the parts or pieces. Because there is one square, as contrasted with mitre, joint at each end of the center leg piece in each sheet of the core of this invention the flux in crossing such square joint is perpendicular to the lengthwise dimension of the center leg piece and it is therefor particularly advantageous to make the center leg piece of doubly oriented material.

While there have been shown and described particular embodiments of the invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention, and therefore y it is intended by the appended claims to cover all such changes and modications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A three-legged laminated magnetic core having similarly constructed alternately reversed superposed edgewise coincident f'lat layers each formed of at least one lamination sheet containing seven lamination pieces, said seven lamination pieces in each sheet comprising seven different lamination patterns all of which are repeated in successive sheets of all layers so that the core is composed of seven different lamination patterns, said lamination pieces of each sheet being equal width relatively thin different length strips `of magnetic material having a most favorable magnetic direction coinciding with their lengthwise dimension and with the normal direction of magnetic flux therein, three of said pieces in each sheet being side by side parallel leg pieces and four of said pieces being yoke pieces extending perpendicular to said leg pieces and bridging the space between corresponding ends of adjacent leg pairs whereby said core has four corner joints between an end of the four yoke pieces and the ends of the two outer leg pieces and two T joints between the other ends of the four yoke pieces and the ends of the center leg piece, each T joint being a mitre joint on one side and a square joint on the other side, the square joints in each layer being on opposite sides of the center leg, all four of said corner joints being mitre joints in each of said layers, the irst of said seven patterns being a generally parallelogram shaped center leg piece with its ends at forty-tive angular degrees to its longitudinal center line and having one corner notched and another corner squared to the same Width as the depth of the notch and on the same side, the second of said seven patterns being a generally isosceles trapezoid shaped first outer leg piece with parallel sides and ends at forty-live degrees to its sides and having its ends adjacent the long side square cut to the same depth, the third of said seven patterns being a generally isosceles trapezoid shaped second outer leg piece with parallel sides and ends at forty-five degrees to its sides and having its ends adjacent the short side notched to the same depth, the fourth of said seven patterns being a yoke piece of the same geometrical shape as the third pattern and joining forty-five degree extending adjacent ends of the first and second patterns, the fifth of said seven parts being a yoke piece of the same geometrical shape as the second pattern and joining forty-five degree extending adjacent ends of the rst and third patterns, the sixth `of said seven patterns being a yoke piece having a square end and a notched corner forty-five degree end joining the other ends of the first and second patterns, the seventh of said seven patterns being a yoke piece having a square end and a square corner fortyfive degree end joining the other ends of the rst and third patterns, the layout of pieces in the sheets of alternate layers being reversed relative to the longitudinal center line of the center leg.

2. A three-legged laminated magnetic core having similarly constructed alternately reversed superposed edge- Wise coincident flat layers each formed of at least one lamination sheet containing seven lamination pieces, said seven lamination pieces in each sheet comprising six different lamination patterns all of which are repeated in successive sheets of all layers so that the core is composed of six different lamination patterns said patterns being equal width relatively thin diterent length strips of magnetic material having a most favorable magnetic direction coinciding with their lengthwise dimension and with the normal direction of magnetic ux therein, three of said pieces in each sheet being side by side parallel leg pieces and four of said pieces in each sheet being yoke pieces extending perpendicular to said leg pieces and bridging the space between corresponding ends of adjacent leg pieces whereby said core has four corner joints between an end of the four yoke pieces and the ends of the two outer leg pieces and two T joints between the other ends of the four yoke pieces and the ends of the center leg piece, each T joint being a mitre joint on one side and a square joint on the other side, the square joints in each layer being on opposite sides of the center leg, all tfour of said corner joints being mitre joints in each of said layers, the rst of said six patterns being the center leg piece and being parallelogram shaped with its ends at forty-tive angular degrees to its longitudinal center line, the second of said six patterns being generally isosceles trapezoid shaped outer leg pieces with parallel sides and ends at forty-five degrees to the sides and having one corner of the long side square cut and the opposite corner of the short side notched to the same depth as the width of the square out, the third of said six patterns being a generally isosceles trapezoid shaped yoke piece having one end linear and the other end notched on the short side, the fourth of said six patterns being a generally isosceles trapezoid shaped yoke piece having one corner square cut at the long side, the fifth of said six patterns being a yoke piece aligned lengthwise with the third pattern and having a square end and a notched beveled end, the sixth of said six patterns being the remaining yoke piece and having a square end and a square corner beveled end, alternate layers being reversed about an axis through the center points of the leg pieces.

3. A three-legged laminated rectangular magnetic core comprising a plurality of fully congruent superposed lamination layers of grain-oriented magnetizable material each formed of at least one sheet of laminations, each said sheet having seven lamination pieces of uniform width consisting of three leg pieces and four yoke pieces, separate pairs of said yoke pieces forming T- joints with opposite ends of the center leg piece, said center leg piece being generally parallelogram shaped whereby said T-joints each comprise a mitre butt joint with one yoke piece and a square butt joint with the other yoke piece of each said pair of yoke pieces with the square joints on opposite sides of said center leg, the side leg pieces of each sheet being generally isosceles trapezoidal in shape and .forming with the adjacent yoke pieces offset mitre butt joints at each outside corner of said core, the mitre joint offset at two adjacent corners defining one outside edge of of said core being opposite in direction to the mitre joint offset at the other two corners, adjacent layers of said core being formed of lamination pieces of the same patterns but with the sheets of laminations in adjacent layers being reversely positioned with respect to a core axis perpendicular to said one outside edge, whereby said core consists of only two different kinds of lamination layers made up of a single set of lamination patterns to provide offset overlap at all said corner joints and transposed mitre overlap at said T-joints.

4. A magnetic core as defined in claim 3 in which the said outside core edge extends between the side legs and the said core axis is the longitudinal axis ofthe center leg.

References Cited by the Examiner UNITED STATES PATENTS 2,407,626 9/46 Welch 336-215 2,792,554 5' 57 Graham 336-5 3,064,220 ll/ 62 Specht 336-217 3,069,643 12/ 62 Stein et al a 336-217 JOHN F. BURNS, Primary Examiner. LARAMIE E. ASKIN, Examiner. 

1. A THREE-LEGGED LAMINATED MAGNETIC CORE HAVING SIMILARLY CONSTRUCTED ALTERNATELY REVERSED SUPERPOSED EDGEWISE COINCIDENT FLAT LAYERS EACH FORMED OF AT LEAST ONE LAMINATION SHEET CONTAINING SEVEN LAMINATION PIECES, SAID SEVEN LAMINATION PIECES IN EACH SHEET COMPRISING SEVEN DIFFERENT LAMINATION PATTERNS ALL OF WHICH ARE REPEATED IN SUCCESSIVE SHEETS OF ALL LAYERS SO THAT THE CORE IS COMPOSED OF SEVEN DIFFERENT LAMINATION PATTERNS, SAID LAMINATION PIECES OF EACH SHEET BEING EQUAL WIDTH RELATIVELY THIN DIFFERENT LENGTH STRIPS OF MAGNETIC MATERIAL HAVING A MOST FAVORABLE MAGNETIC DIRECTION COINCIDING WITH THEIR LENGTHWISE DIMENSION AND WITH THE NORMAL DIRECTION OF MAGNETIC FLUX THEREIN, THREE OF SAID PIECES IN EACH SHEET BEING SIDE BY SIDE PARALLEL LEG PIECES AND FOUR OF SAID PIECES BEING YOKE PIECES EXTENDING PERPENDICULAR TO SAID LEG PIECES AND BRIDGING THE SPACE BETWEEN CORRESPONDING ENDS OF ADJACENT LEG PAIRS WHEREBY SAID CORE HAS FOUR CORNER JOINTS BETWEEN AN END OF THE FOUR YOKE PIECES AND THE ENDS OF THE TWO OUTER LEG PIECES AND TWO T JOINTS BETWEEN THE OTHER ENDS OF THE FOUR YOKE PIECES AND THE ENDS OF THE CENTER LEG PIECE, EACH T JOINT BEING A MITRE JOINT ON ONE SIDE AND A SQUARE JOINT ON THE OTHER SIDE, THE SQUARE JOINTS IN EACH LAYER BEING ON OPPOSITE SIDES OF THE CENTER LEG, ALL FOURT OF SAID CORNER JOINTS BEING MITRE JOINTS IN EACH OF SAID LAYERS, THE FIRST OF SAID SEVEN PATTERNS BEING A GENERALLY PARALLELOGRAM SHAPED CENTER LEG PIECE WITH ITS ENDS AT FORTY-FIVE ANGULAR DEGREES TO ITS LONGITUDINAL CENTER LINE AND HAVING ONE CORNER NOTCHED AND ANOTHER CORNER SQUARED TO THE SAME WIDTH AS THE DEPTH OF THE NOTCH AND ON THE SAME SIDE, THE SECOND OF SAID SEVEN PATTERNS BEING A GENERALLY ISOSCELES TRAPEZOID SHAPED FIRST OUTER LEG PIECE WITH PARALLEL SIDES AND ENDS OF FORTY-FIVE DEGREES TO ITS SIDES AND HAVING ITS ENDS ADJACENT THE LONG SIDE SQUARE CUT TO THE SAME DEPTH, THE THIRD OF SAID SEVEN PATTERNS BEING A GENERALLY ISOSCELES TRAPEZOID SHAPED SECOND OUTER LEG PIECE WITH PARALLEL SIDES AND ENDS OF FORTY-FIVE DEGREES TO ITS SIDES AND HAVING ITS ENDS ADJACENT THE SHORT SIDE NOTCHED TO THE SAME DEPTH, THE FOURTH OF SAID SEVEN PATTERNS BEING A YOKE PIECE OF THE SAME GEOMETRICAL SHAPE AS THE THIRD PATTERN AND JOINING FORTY-FIVE DEGREE EXTENDING ADJACENT ENDS OF THE FIRST AND SECOND PATTERNS, THE FIFTH OF SAID SEVEN PARTH BEING A YOKE PIECE OF THE SAME GEOMETRICAL SHAPE AS THE SECOND PATTERN AND JOINING FORTH-FIVE DEGREE EXTENDING ADJACENT ENDS OF THE FIRST AND THIRD PATTERNS, THE SIXTH OF TSAID SEVERN PATTERNS BEING A YOKE PIECE HAVING A SQUARE END AND A NOTCHED CORNER FORTY-FIVE DEGREE END JOINING THE OTHER ENDS OF THE FIRST AND SECOND PATTERNS, THE SEVENTH OF SAID SEVEN PATTERNS BEING A YOKE PIECE HAVING A SQUARE END AND A SQUARE CORNER FORTYFIVE DEGREE END JOINING THE OTHER ENDS OF THE FIRST AND THIRD PATTERNS, THE LAYOUT OF PIECES IN THE SHEETS OF ALTERNATE LAYERS BEING REVERSED RELATIVE TO THE LONGITUDINAL CENTER LINE OF THE CENTER LEG. 